Effect of smoking intensity on thyroid volume, thyroid nodularity and thyroid function: the Melen study.

AIM: The purpose of our study was to determine the association between smoking habit, goiter, thyroid functions and ultrasonographic nodularity in moderately iodine deficient area.

METHODS: The MELEN study is a prospectively designed survey on the prevalence of thyroid diseases in Turkish adults. A total of 2298 subjects with a mean age of 50 (age range 18 to 92) were interviewed. Smoking habits were registered from questionnaires and subsequent interviews with a physician. Thyroid ultrasonography was performed and interpreted by the same experienced physician, using the same equipment. After an overnight fast, blood samples were collected from all the study subjects for the determination of serum free thyroxine, thyroid stimulating hormone (TSH) were measured.

RESULTS: Mean thyroid volumes of current smokers were significantly lower than either former or never smokers (P=0.014). There were no difference according to smoking habits on goiter and established multinodularity in current smokers (P<0.05). Heavy smokers (>20 pack/year) had higher thyroid volumes, higher goiter and multinodular goiter (MNG) prevalence than moderate smokers (P<0.001). Thyrotoxicosis (TSH<0.35) cases were more frequent among heavy smokers than moderate smokers (14.1% versus 8.2%, P<0.001; respectively). Heavy smoking independently predicted goiter (odds ratio: 1.459 [95% confidence interval: 1.029 and 2.068]; P=0.034).

CONCLUSION: Heavy smoking was associated with increased prevalence of thyroid multinodularity and goiter in respect to moderate smoking. No association was found between smoking habit and thyroid dysfunction.